This invention relates to the field of breathing apparatus and particularly relates to respiratory protective systems such as may be used after some emergency situation has caused a noxious environment.
For example, this invention may be used as a mine catastrophe respirator system. This invention will be described with particular reference to systems usable by miners. However, it is to be understood that this invention is applicable to other fields where extended use for protection from noxious environments may be necessary. The description in terms of miners' equipment and problems is merely for purposes of illustration.
There are three significant reasons which justify the need for respiratory protection of the type given by this invention. The presence of elevated levels of noxious gases which may be present in a mine following some sort of disaster, including deadly carbon monoxide if there has been a fire, is an immediate hazard to trapped miners. Furthermore, trapped miners, especially if there has been a fire, suffer from a reduced oxygen supply. Therefore, oxygen must be supplied along with protection from the noxious constituents of the surrounding atmosphere. Thirdly, if oxygen is to be supplied for periods longer than 2 or 3 hours, the respiratory protective device used must be of a type which controls the oxygen concentration of the gas which is breathed. Too high a concentration of oxygen breathed for long periods of time causes hypoxia. Therefore, the supply of gas must also include another gas, such as nitrogen, to ensure that, even in the presence of leaks from the system, the oxygen concentration can be controlled.
A significant economic and logistic savings can be realized if one device to be used in emergency situations can be kept near a small group of miners instead of giving each miner his own device. Such a device should be capable of supplying, for example, about five or six miners with a 2-day supply of breathable gas for a period during which they await rescue. This would require a supply of 10 or 12 man-days of breathable gas.
Respirator systems of the prior art which supply oxygen and protect the user from a noxious environment are of two basic types. One is a compressed air system and the other is an oxygen rebreather system.
A compressed air system consists of a compressed air tank with a demand regulator which provides air to a mask during inhalation. The major problem of a system of this type is that the immense volume and weight of the supply tank which would be required for extended use prohibits the use of such a system for such applications.
An oxygen rebreather system includes a significantly smaller tank containing pure oxygen. Pure oxygen is supplied to a breathing bag and a scrubber removes carbon dioxide from the exhaled gas. Some nitrogen is present in the bag at the beginning of use but system leaks soon drive the oxygen concentration of the gas in the bag to near 100 percent. Prolonged use of a respirator prohibits the use of a standard oxygen rebreather system for such applications because of the aforementioned hypoxia.